The present invention relates to quad flat no-lead (QFN) microchip package fabrication processes, and in particular, to extending the life of cutting blades used in QFN package fabrication processes.
Existing QFN packages are often made using the following procedure. A lead frame is provided. Often the lead frame has a special tape on one side. The tape is used for wire bond vacuum and to provide support for the lead frame. Next, the dies are placed on the lead frame, and wire bonding is performed. Then, a molding compound is applied to encapsulate the lead frame, the dies, and the wire leads. Finally, the encapsulated dies are sawed apart into individual QFN package units.
The thickness of current lead frames may vary; common thicknesses include 0.127 um, 0.152 um, and 0.203 um. The lead frame material may be a copper alloy material such as Olin C7025. The special tape used may vary as well. Common types of tape include Nitto tape and Hitachi tape.
A number of problems arise from the above-described fabrication process. First, problems arise relating to the special tape. If the lead frame includes one type of special tape, the tape often outgases due to the temperatures involved in the wire bonding process, and the outgas negatively affects the wire bonding quality. If the lead frame includes another type of special tape, warpage issues arise during lead frame production.
Second, since the lead frame is encapsulated within the molding compound, during the sawing process the saw must also cut the lead frame. The metal structure of the lead frame reduces the lifespan of the saw blade.
Third, sawing the metal lead frame often results in burrs. Burrs are undesirable because they may cause quality and reliability issues when the device is used on the circuit board. Specifically, the burrs may contribute to short circuits during device testing.
Thus, there is a need for an improved QFN package fabrication processes. The present invention solves these and other problems by using a different type of lead frame.